Strongest Evidence to Date About Common Genetic Roots of Mental Illness

August 20, 2013. Something about genes and the way they vary slightly from person to person increases the chances that some people will develop a psychiatric disorder such as autism, ADHD, bipolar disorder, depression, or schizophrenia. A new, multinational study of more than 75,000 people, led by Naomi Wray of the University of Queensland, Brisbane, Australia, and Kenneth Kendler of Virginia Commonwealth University, Richmond, strongly supports previous hints that these different disorders have common genetic roots.

By looking at the patterns of commonly found single-letter changes (called common variants) in the DNA of each person, first author Sang Hong Lee and colleagues found that not only did each individual disorder carry its own “genomic signature,” but also parts of these signatures were shared between disorders. For example, the common variants of people with schizophrenia and bipolar disorder were more similar than either of the disorders compared to people without a psychiatric disorder. Surprisingly, given previous evidence and the nature of their symptoms, schizophrenia and MDD were found to be somewhat similar in the "genomic signature" of their common DNA variants.

The results begin to put numbers on the genetic overlaps hinted at by previous family studies and may help to sort out the relative contributions of genes and environment (the famous nature vs. nurture debate). Though many of these previous studies have found increased risk for one mental disorder in a first-degree relative (parent, sibling, or child) of someone with a different disorder, this could reflect shared environment or shared genes. The new results, based entirely on genetic data from unrelated people, indicate a clear contribution by genetic factors. They also support the idea that vulnerability to different disorders can stem from the same biology. (For more details, see the related news story.)—Michele Solis.